Department of Nuclear Engineering, Texas A&M University, 337 Zachry Engineering Center, 3133 TAMU, College Station, TX 77843-3133, USA.
Phys Med Biol. 2014 May 7;59(9):2285-305. doi: 10.1088/0031-9155/59/9/2285. Epub 2014 Apr 15.
The present state of modeling radio-induced effects at the cellular level does not account for the microscopic inhomogeneity of the nucleus from the non-aqueous contents (i.e. proteins, DNA) by approximating the entire cellular nucleus as a homogenous medium of water. Charged particle track-structure calculations utilizing this approximation are therefore neglecting to account for approximately 30% of the molecular variation within the nucleus. To truly understand what happens when biological matter is irradiated, charged particle track-structure calculations need detailed knowledge of the secondary electron cascade, resulting from interactions with not only the primary biological component-water--but also the non-aqueous contents, down to very low energies. This paper presents our work on a generic approach for calculating low-energy interaction cross-sections between incident charged particles and individual molecules. The purpose of our work is to develop a self-consistent computational method for predicting molecule-specific interaction cross-sections, such as the component molecules of DNA and proteins (i.e. nucleotides and amino acids), in the very low-energy regime. These results would then be applied in a track-structure code and thereby reduce the homogenous water approximation. The present methodology-inspired by seeking a combination of the accuracy of quantum mechanics and the scalability, robustness, and flexibility of Monte Carlo methods-begins with the calculation of a solution to the many-body Schrödinger equation and proceeds to use Monte Carlo methods to calculate the perturbations in the internal electron field to determine the interaction processes, such as ionization and excitation. As a test of our model, the approach is applied to a water molecule in the same method as it would be applied to a nucleotide or amino acid and compared with the low-energy cross-sections from the GEANT4-DNA physics package of the Geant4 simulation toolkit for the energy ranges of 7 eV to 1 keV.
目前在细胞水平上对放射性诱导效应进行建模的方法没有考虑到非水成分（即蛋白质、DNA）的核微观非均质性，而是将整个细胞核近似为均质的水介质。因此，利用这种近似进行带电粒子径迹结构计算忽略了核内大约 30%的分子变化。为了真正了解生物物质受到照射时会发生什么，带电粒子径迹结构计算需要详细了解与初级生物成分（水）以及非水成分相互作用而产生的次级电子级联的知识，直至非常低的能量。本文介绍了我们在计算入射带电粒子与单个分子之间低能相互作用截面的通用方法方面的工作。我们的工作目的是开发一种自洽的计算方法，用于预测特定分子的相互作用截面，例如 DNA 和蛋白质的组成分子（即核苷酸和氨基酸）在非常低的能量范围内。然后，这些结果将应用于径迹结构代码中，从而减少对均质水的近似。本方法的灵感来自于寻求量子力学的准确性与蒙特卡罗方法的可扩展性、鲁棒性和灵活性相结合，从计算多体薛定谔方程的解开始，然后使用蒙特卡罗方法计算内部电子场的微扰，以确定相互作用过程，如电离和激发。作为对我们模型的测试，该方法应用于水分子，其方法与应用于核苷酸或氨基酸相同，并与 GEANT4 模拟工具包中的 GEANT4-DNA 物理包的低能截面进行比较，能量范围为 7 eV 至 1 keV。
